Or HaChaim on Numbers 7:89/אור החיים על במדבר ז׳:פ״ט

1 הקול מדבר אליו, the Voice speaking to him, etc. We have already explained on Exodus 20,1 that when G'd speaks an angel is created as a result of such speech and it is the voice of that angel which man (prophet) hears. I have explained all the instances in which the word לאמור appears as unnecessary such as when G'd's message to Moses or Aaron is introduced. This is what is meant here when the Torah speaks of "the Voice" speaking to Moses. The Torah underlines that in this instance G'd's voice spoke to Moses directly, not the voice of an angel. Although there is a dagesh in the letter ד to tell us that the meaning is מתדבר, i.e. the voice itself was doing the talking, it was not the projection of someone else "behind" the voice. This form is grammatically admissible; the intelligent reader will understand what I mean.